New impregnation mixtures for electrical insulating mixtures

ABSTRACT

Dielectric liquids are provided consisting essentially of a mixture of 25 - 33 parts of monochlorinated diphenyl, 28 - 36 parts of 2,4&#39;&#39;-dichlorodiphenyl and 37 - 43 parts by weight of trichlorodiphenyl.

United States Patent 1 Jay 11 3,844,968 [451 Oct. 29,1974

[ NEW IMPREGNATION MIXTURES FOR ELECTRICAL INSULATING MIXTURES [75] Inventor: Pierre Jay, Saint Didier au Mont dOr, France [73] Assignee: Rhone-Progil, Paris, France [22] Filed: Feb. 3, 1972 [21] Appl. N0.: 223,319

[30] Foreign Application Priority Data France 71.04692 UNITED STATES PATENTS 3,038,107 6/1962 Weingarten 252/66 3,068,297 12/1962 Weingarten 252/66 3,072,728 1/1963 Kosmin et al. 260/612 R 3,194,766 7/1965 Coquillion 252/66 FOREIGN PATENTS OR APPLICATIONS 702,497 1/1931 France 252/60 Primary ExaminerJohn D. Welsh Attorney, Agent, or FirmBr0wdy and Neimark [57] ABSTRACT Dielectric liquids are provided consisting essentially of a mixture of 25 33 parts of monochlorinated diphenyl, 28 36 parts of 2,4'-dichlor0diphenyl and 37 43 parts by weight of trichlorodiphenyl.

7 Claims, No'Drawings products with 41, 48 or 54 percent by weight of chlorine have been, successfully used for impregnating paper condensers, their fairly high permittivity enabling condensers to be produced which have relatively small dimensions and which are of very high quality. These conventional chlorinated diphenyls are, however, complex mixtures, the product with 41 percent chlorine containing mainly dichlorodiphenyls, t'richlorodiphenyls and tetrachlorodiphenyls in the form of varying isomers, even though the quantity 41 percent chlorine corresponds to 3 chlorine atoms per molecule.

Among the separated fractions of the polychlorinated diphenyls, dichlorodiphenyl fractions and trichlorodiphenyl fractions are particularly interesting because of their high permittivity. On the other hand, the tetrato hexachlorinated homologs have reduced dielectric constant values, such values decreasing as the number of chlorine atoms linked to the diph'enyl molecule increases; however, these higher chlorinated homologs do have. sufficiently high dielectric constant values for such products to find application as dielectric impregnants, particularly in admixture with the lower chlorine containing homologs.

The polychlorinated diphenyls in general possess a number of advantages in this field, one of the prime such advantages being great chemical stability. However, such compounds also possess several disadvantages. Thus, dichlorodiphenyls, for example, are crystallizable which prevents their use in electrical devices operating at low temperature. Trichlorodiphenyls and the higher chlorine containing homologs do not crystallize, but they are considerably more viscous than the dichlorinatetl diphenyls which provides serious problems in attempting to impregnate the dielectric spacers, particularly when such spacers are not easily wettable.

It is known that metallized-paper capacitors and polyolefin film capacitors have several advantages over capacitors of the classical type made with paper. In particular, the polyolefin film capacitors have a very high dielectric strength, but the polyolefin films are not easily wettable with the usual impregnating liquids, such as trichlorodiphenyl. and as a result have not in general been satisfactory because they do not wet sufficiently and the dielectric does not penetrate. In French Patent No. l,502,22l (Nov. 18, I966), there is disclosed the use of trichlorodiphenyl as an impregnating liquid for solid polyolefin spacers, but as pointed out above, this is not satisfactory. In order to obtain improvement in this area, it is proposed in US. Pat. No. 3,483,452 (Sept. I1, 1968) to dissolve atactic polypropylene in the trichlorodiphenyl, but this also does not produce entirely satisfactory results.

It is also known in the art that dielectric liquids consisting of a mixture of polychlorinated diphenyls and trichlorobenzenes have a low viscosity and a low freezing point. On the other hand, such mixtures have a much less satisfactory stability than do chlorodiphenyls, and, moreover, such mixtures have the disadvantage of having a high vapor pressure.

It is, accordingly, an object of the present invention to overcome the deficiencies of the prior art, such as indicated above.

It is another object of the present invention to provide for improved electrical capacitors.

It is another object of the present invention to provide new liquid mixtures used for impregnating electrical insulated materials.

It is another object of the present invention to provide new dielectric compositions especially suitable for impregnating polyolefin dielectric elements.

In attaining the above and other objectives, there have now been provided new liquid compositions for impregnating electrical insulating materials which obviate and avoid the abovementioned difficulties and which provide excellent permittivity and good chemical stability, as well as low viscosity, low freezing point,

low vapor pressure and which are not crystallizable.

These compositions, which are applicable in a general way to usage in all insulated electrical devices, have shown'particular usefulness in the impregnation of dielectric materials which are normally very difficult to wet, such as polyolefin materials, and those which are used in low temperature environments.

The new dielectric liquid compositions consist essentially of a mixture of various diphenyl chlorination products in specified proportions, namely for parts by weight, from 25 33 parts of monochlorodiphenyl, from 28 36 parts by weight of 2,4-dichlorodiphenyl, and from 37 43 parts by weight of trichlorodiphenyl.

The present invention has a number of surprising aspects, one of which is that the monochlorodiphenyl product may be used in the substantial quantities indicated and that it not only does not detract from the properties of the composition, but adds to such proper ties. Thus, in the prior art it was most often accepted that the monochlorodiphenyl homolog was not satisfactory as a capacitor impregnant. Since this material is crystallizable, it could not be expected that one could use substantial quantities'of this material and obtain a liquid which would not crystallize. In fact, other workers have tried to utilize mixtures containing this compound, noting for example French Patent No. 702,497 (Sept. 24, 1930) which describes a composition containing 45 percent of trichlorodiphenyl and 55 percent of a eutectic mixture of orthoand para(mono)- chlorodiphenyl. It has been confirmed that such a composition is not satisfactory and, indeed, applicants own tests have shown that, when such a mixture is cooled, crystals deposit slowly and the mixture finally solidifies at 20C. A composition having such properties is not suitable for the intended usage.

The monochlorodiphenyl to be used in accordance with the present invention may be any chlorinated diphenyl product, the chlorine content of which is at or near 1 chlorine atom per diphenyl molecule, and having only been subjected to a distillation to remove any tar. In other words, it is not necessary to utilize a pure isomer or to provide the monochlorodiphenyl in purified form.

With regard to the 2,4-dichlorodiphenyl fraction, it is to be understood that any chlorinated diphenyl fraction, the total chlorine content of which corresponds to a proportion of about 2 chlorine atoms per diphenyl molecule, and in which the 2,4-isomer is present in a quantity of at least 50 percent by weight, is satisfactory. Though the use of a pure 2,4-dichlorodiphenyl is not excluded from the present invention, it is preferred that the 2,4-dichlorodiphenyl fraction utilized in the present invention constitute in fact 65 85 percent by weight of the 2,4 isomer rather than 100 percent thereof. According to a particularly advantageous form of the invention, there is used a diphenyl chlorination product distilling between 154 164C. under a pressure of mm. of mercury, this distillation product containing 75 percent by weight of the pure 2,4 isomer. Reference may be made to Pat. No. 3,194,766 which discloses various types of 2,4-dichlorodiphenyl fractions which are utilizable in the present composition.

The trichlorodiphenyl component used in the present invention has a chlorine content at or near 3 chlorine atoms per diphenyl molecule, i.e., it contains approximately 41 percent chlorine and has been treated to the extent that the chlorination tars have been removed as in the case of the monochlorodiphenyls discussed above. This is the same trichlorodiphenyl used in the prior art for impregnation of capacitors. Processes for obtaining this material are also found in Pat. No. 3,194,766.

The new dielectric impregnating liquids are provided in a single mixture, at room temperature, consisting essentially of the three constituents in suitable proportions; the liquids are preferably treated in accordance with the classical activated earth treatment. The viscosity of the composition is lower than the classical trichlorodiphenyl impregnating liquid and, in general, if this characteristic is considered in relation to temperature it may be said that the viscosity of the mixture according to the present invention is similar to the viscosity of trichlorodiphenyl taken at a temperature higher than the temperature of the mixture in accordance with the present invention. This reduced viscosity is an important advantage.

Another surprising advantage of the present composition is its wetting power. There was no reason to predict that the wetting power of the composition would be better than the wetting power of the components, yet with regard to solid dielectric materials, particularly polyolefin films, it has been surprisingly found that the wetting power of the present composition is far superior to that of trichlorodiphenyl. This wetting power may be evaluated by measuring contact angle of a liquid drop with a polyolefin film on which the drop is deposited; this is the angle between the surface of the film and the tangent to the curve of the drop at the contact point of the drop at the film. lt has been observed that for the mixture in accordance with the present invention, this angle is 39, while it is 48 for a drop of trichlorodiphenyl.

The penetrating power into a polyolefin film of the film and an open tube above it, while maintaining good sealing. The liquid to be tested was poured into the tube and the temperature was brought to C. by means of an electrical resistance followed by stirring to obtain a good uniform temperature. The liquid was thus maintained at 100C. for 2 hours and then the temperature was gradually increased 10 at a time over each subsequent 2 hour period, with the results being tabulated below at each temperature increment. The test was conducted under identical conditions for the two liquid impregnants, namely the impregnant in the composition of the present invention and trichlorodiphenyl. For the impregnant of the present invention there was used a mixture of 27 percent monochlorodiphenyl, 36 percent dichlorodiphenyl with 60 percent of the 2,4 isomer, and 37 percent trichlorodiphenyl. The weight of liquid recovered in the lower receptacle, at the end of each temperature increment, constitutes the measure of liquid penetrating power through the polypropylene film.

Weight of recovered liquid. in mg. after the stage at:

On the basis of the above test, it is seen that the composition of the present invention has greatly superior penetrating power with regard to polyolefin film.

It is also found in accordance with the present invention that the dielectric properties of the impregnant of the present invention are very satisfactory. The permittivity of these impregnants at 20C. is very near 6 and their dielectric losses are low. For example, a mixture according to the invention, with a density of 1.29 and a viscosity of 1.6 centistokes at 100C. has a loss angle (tg5), measured at 100C. and under 50 Hertz, of 0.005.

When the dielectric liquids are intended to be used to impregnate polyolefin film capacitors, it may be advantageous to add with them a low quantity of a silicone oil, soluble therein, which results in the decreasing of the surface tension of the mixture and improves wetting even further. The selection of any particular silicone oil is not critical and, in general, one may choose any known product from the thinnest to the most viscous, provided that this silicone oil is entirely soluble in the mixtures according to the present invention in the. designated proportions. For example, polymethylphenyl siloxanes are particularly suitable and among'these compounds it is preferred to select those having a sufficiently low vapor pressure so that they are not removed by vaporization during the dielectric liquid degassing which takes place before impregnating the capacitors.

The quantity of silicone oil which may be added is also not particularly critical, except that the maximum quantity must not be so great that the silicone oil will be in effect a diluent; in a general way, the quantity of silicone oil used will generally be between 20 and 2,000 parts per million (ppm) with regard to the polychlorodiphenyl mixture. Based on tests conducted on mixtures according to the present invention and with added parts of silicone oil, the contact angle defined above was reduced to 25, 23, and 16 for silicone quantities added to the impregnant compositions of respectively 200, 500, 1,000 and 2,000 ppm.

It is also possible to incorporate into the impregnant compositions of the present invention any of the usual additives and adjuvants, such as purifiers, which are normally used in such dielectric liquid compositions.

With regard to the purifiers, for example, these may be materials which combine with degradation products of the chlorinated diphenyls, under the action of electrical field; for example, hydrochloric acid may result from the degradation under electrical field of the chlorinated diphenylcompounds and the purifier adjuvants, often referred to as scavengers, are capable of reacting with the hydrochloric acid and thereby obviating its potential damaging effects. Among such purifiers or scavengers may be mentioned amines, morpholine derivatives, antimony and tin organic compounds and epoxide compounds. Such epoxide compounds are particularly advantageous, particularly phenoxy-propylene, styrene oxide, diphenyl-ethylene oxide, epoxyethyl-l-epoxy- 3,4-cyclohexane, etc. These additives may be incorporated without any disadvantage in mixtures according to the present invention and normal proportions, i.e., in quantities between 0.1 and 5 percent by weight with regard to the chlorinated diphenyl mixture.

The liquid dielectric mixtures of the present invention have advantageous utility in all the normal applications of such liquids including, in a general way, electrical device insulation by means of impregnation. They are particularly useful in the treatment of materials subject to hard running conditions or materials which are difficult to impregnate with other liquid mixtures, such as for example, devices exposed at low temperatures, or capacitors having one or several polyolefin films which may or may not be used in conjunction with the conventional dielectric paper sheets.

The methods of treating the electrical devices with the liquids of the present invention are the same methods as are normally used with the chlorinated diphenyl materials. For example, for capacitors having polyolefin film, after the usual drying cycle, the films may be impregnated with the dielectric liquid composition, such as by the use of vacuum, followed by heating for several hours at a temperature from 85 95C. It is a feature of the present invention, because of the special properties of the dielectric liquid compositions of the present invention that the impregnation may be achieved at a significantly lower temperature than that which has been utilizable in the past; for example, one may impregnate the capacitor using the composition of the present invention at only 60C., and this is substantially less than the temperature which may be used if one is attempting to impregnate using a viscous liquid such as trichlorodiphenyl.

The quality of the resulting impregnated devices are, in a general way, better than the properties of the impregnated devices obtained with the impregnation liquids of the prior art. The capacity, the insulating resistance, and the aging properties are more than adequate for the various dielectric requirements.

The present invention will be better understood by reference to the following specific examples, given in a non-limitative manner, which further illustrates the invention as well as its further objectives, and which emphasize the characteristics of condensers and capacitors impregnated with the composition of the present invention.

EXAMPLE 1 A dielectric liquid according to the present invention was prepared by mixing, at room temperature, the following products in the indicated proportions:

Monochlorodiphenyl 30% by wt. Dichlorodiphenyl with 757' of the 2,4 isomer 30% by wt. Trichlorotliphenyl 40% by wt.

This mixture had a total chlorine content of 33%. Its viscosity was 16 centistokes at 20C.; 3.6 centistokes at 60C.; 1.6 centistoke at l0OC. lts permittivity was 6.0 at 20C. Cooled to --C., it did not crystallize, even after priming or seeding.

This mixture was used to impregnate a series of 10 capacitors. Those had aluminum frames separated by an insulating set composed of two polypropylene films 12 microns thick, placed on every side of a Kraft paper sheet for capacitors, having a thickness of IO microns. lmpregnation was made at C., under a pressure of 10' mm. Hg. after drying. Then the devices were maintained at 90C. for 4 hours under a normal pressure.

The dielectric losses of these capacitors were measured at room temperature, at the frequency of 50 Hz and under a tension of 1300 volts. It was observed that they varied little from one capacitor to another. The average values obtained on the whole of devices were;

tg 5 it)" immediately after impregnation tg 6 10 after a 500-hrs ageing, under I920 volts 8.l

EXAMPLE 2 As a comparison, capacitors impregnated either with a liquid according to the invention, or with trichlorodiphenyl were submitted to a test of dielectric rigidity under continuous voltage.

For this were prepared series of 60 capacitors having aluminum frames separated by a polypropylene insulating film 12 microns thick. After drying, 30 of those devices were impregnated under a pressure of 10' mm. Hg, at C., with trichlorodiphenyl, and at 60C. the other 30 devices were impregnated with the mixture according to invention, as in example I, to which were added 100 parts per million of silicone oil, a methylphenylpolysiloxane having a viscosity of I 200 centistokes at 20C. and a flammability point of 265C.; this operation was followed with a heating of the devices at C. for 4 hours at atmospheric pressure.

Then the capacitors were placed under continuous voltage which was progressively increased at the rate of 0.5 kv/sec., until every device was put out of use. The voltage at which each capacitor breakdown occurred was noted and breakdown voltage average value of the two series was calculated. In Table 2 below, minimal and maximal voltages for breakdown taken in every lot of condensers, and calculated average values of breakdown voltage, are given.

The above figures emphasize the superiority of dielectric liquids according to the present invention, with regard to trichlorodiphenyl. superiority which corresponds to a better dielectric rigidity of capacitors impregnated by means of the present liquids. Average value and breakdown minimal voltage are especially significant.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is described in the specification.

What is claimed is:

l. A liquid composition for the impregnation of electrical insulating materials consisting esentially of a mixture of 25 33 parts by weight of monochlorodiphenyl, 28 36 parts by weight of dichlorodiphenyl consisting of at least 50 percent of the 2,4 isomer, and 37 43 parts by weight of trichlorodiphenyl. v

2. A composition in accordance with claim 1 in which said dichlorodiphenyl consists of 65 percent by weight of said 2,4 isomer.

3. A composition in accordance with claim 2 wherein said dichlorodiphenyl is a diphenyl chlorination product distilling between 154 and l64C. under a pressure of 10 mm. Hg. and containing 75 percent by weight of 2,4'-dichlorodiphenyl.

4. A composition in accordance with claim 1 further comprising 20 2,000 ppm based on said parts by weight of a silicone oil.

5. A composition in accordance with claim 4 wherein said silicone oil is a methylphenylpolysiloxane.

6. A composition in accordance with claim 1 further comprising 0.] 5 percent by weight based on said I00 parts of a hydrochloric acid scavenger.

7. A composition in accordance with claim 6 wherein said scavenger is an epoxide compound.

* i= l =l= 

1. A LIQUID COMPOSITION OF THE IMPREGNATION OF ELECTRICAL INSULATING MATERIALS CONSISTING ESSENTIALLY OF A MIXTURE OF 25 33 PARTS BY WEIGHT OF MONOCHLORODIPHENYL, 28 - 36 PARTS BY WEIGHT OF DICHLORODIPHENYL CONSISTING OF AT LEAST 50 PERCENT OF THE 2,4'' ISOMER, AND 37 - 43 PARTS BY WEIGHT OF TRICHLORODIPHENYL.
 2. A composition in accordance with claim 1 in which said dichlorodiphenyl consists of 65 - 85 percent by weight of said 2, 4'' isomer.
 3. A composition in accordance with claim 2 wherein said dichlorodiphenyl is a diphenyl chlorination product distilling between 154* and 164*C. under a pressure of 10 mm. Hg. and containing 75 percent by weight of 2,4''-dichlorodiphenyl.
 4. A composition in accordance with claim 1 further comprising 20 - 2,000 ppm based on said 100 parts by weight of a silicone oil.
 5. A composition in accordance with claim 4 wherein said silicone oil is a methylphenylpolysiloxane.
 6. A composition in accordance with claim 1 further comprising 0.1 - 5 percent by weight based on said 100 parts of a hydrochloric acid scavenger.
 7. A composition in accordance with claim 6 wherein said scavenger is an epoxide compound. 